The present invention relates to video measurements, and more particularly to a relative channel delay measurement that is robust in the presence of random noise, compressed video impairments, etc. and may be performed in-service using regular program material.
In the television arts it is of interest to use an automated method to measure the relative delay between pairs of channels among the three components of component analog video and equivalent digital representations. An example is the delay between Y and Pb channels for Y,Pb,Pr component video. Prior measurement methods measure the relative position of either specific edges of a specific part of a line of the video signal, such as the green/magenta transition in a video color bars signal, or the null of the sum or differences of sinusoids with slightly different frequencies, as in the Bowtie signal (see U.S. Pat. No. 4,829,366). In both cases specific signals are used and a small portion of the video line is used to make the measurement. Though these methods are intuitive and practical for manual measurements with a video waveform display, both methods are relatively susceptible to noise interference and are not in-service measurements in that special test signals are used. Also neither method allows for convenient determination of delay at different frequencies or average delays over different bandwidths. Further, automated versions of these methods do not inherently give a figure of merit reflecting the probable inaccuracy of the measurement due to impairments or noise present in the video signal.
Another method does use real program material (see U.S. Pat. No. 4,792,846), detects edge transitions in the components of the program material, and uses one component as a reference channel. The relative time difference between the midpoints of the edge transitions averaged over several transitions determines the amount of channel delay of the other two channels with respect to the reference channel, which delay may be used to resynchronize the channels. However this method also is susceptible to noise and does not inherently give a figure of merit reflecting the probable inaccuracy of the time delay measurements due to impairments or noise in the video signal.
What is desired is to have one method of measurement that is robust in the presence of random noise, compressed video impairments, etc. and may be performed in-service using regular program material. It is also desired to determine a figure of merit correlated to the probable accuracy of the measurement due to impairments, such as those resulting from video compression, and/or noise. Finally it is desired to have a method that works with any component video signal—YPbPr, RGB, high definition, standard definition, computer video, etc.—and with variable sample rates which are not necessarily known a priori or are not related to the clock rate of the corresponding digital video.